| 摘要 |
PROBLEM TO BE SOLVED: To provide a switching power supply unit that is capable of preventing a power factor from being degraded even under such a state that a maximum frequency limit of switching frequencies is added at a light load.SOLUTION: The switching power supply unit, obtaining a predetermined output voltage by switching an input voltage through a switching element, includes: ON width control means that controls an ON width of the switching element; zero current detection means that turns on the switching element; frequency reduction means that delays turn-on timing of the switching element to reduce a switching frequency of the switching element when load state detection means detects a light load state; and AC cycle detection means that detects a cycle of the input voltage and keeps a load detection state by the load state detection means constant for each detected cycle. |
